Wallpaper is used to decorate the interior walls of homes, hotels, offices, hospitals and other structures where people live, work and meet. A typical wall is made from a plaster or, in the case of drywall, a gypsum core covered on its major surfaces with paper.
The wallpaper is held to a wall by an adhesive that bonds the wallpaper to the wall. The adhesive can be applied to the wallpaper or to the wall by the person hanging the wallpaper or it can be applied to the wallpaper by the wallpaper manufacturer (e.g., pre-pasted wallpaper), and rehydrated with an activator by the wallpaper hanger prior to hanging. A wallpaper activator is an adhesive that is often used with pre-pasted wallpaper, such that the activator converts the dry pre-pasted wallpaper into wet, tacky pasted wallpaper that is prepared to efficiently adhere to the wall. The adhesives currently in use in the wallpaper industry include wallpaper adhesives (paste), and wallpaper activators.
When applying wallpaper to a wall, it is often advantageous to use a wallpaper primer to prepare the wall for better adherence of the wallpaper. Benefits of using a primer include sealing the surface of the wall to create a surface with a uniform porosity and water resistance and to fix certain defects in the surface of the wall. For example, Liquid Drywall™ (Roman Adhesives, Calumet City, Ill.) is a primer designed to fill in any defects in the surface of the wall and seal the wall to allow wallpaper to be pasted to the entire surface of the wall. For best results, a primer should not only be applied over an entire wall surface, but it should also be applied evenly, in a substantially uniform thickness.
When applying wallpaper it is important to ensure that the adhesive or primer is applied evenly to the wall or to the wallpaper such that there are no areas of the wall or wallpaper that are free of adhesive or primer, that the adhesive or primer is applied in a uniform thickness to the surface of the wall or wallpaper, and that the adhesive or primer has not prematurely dried prior to applying the wallpaper to the wall. When wallpaper is applied, judgment is required in determining whether (1) enough adhesive has been applied so that the entire wall or wallpaper remains wet and sticky upon contact of the wallpaper with the wall; and (2) the adhesive or primer has been applied evenly over the entire surface of the wall or wallpaper. Gruenberger, et al., U.S. Pat. No. 4,293,458, discloses applying a colored or tinted paste to assure complete coating of an adhesive, however, adding a permanent color to an adhesive (or primer) has the disadvantage of permanently coloring the wall or wallpaper which may be visually detected on the face (room-facing) side of the wallpaper, thereby detracting from the wallpaper aesthetics.
There exists a need in the art for a wallpaper adhesive and a primer that provide (1) a visual indication that a sufficient amount or thickness of adhesive or primer has been applied to the wall or wallpaper, (2) a visual indication of a uniform thickness of the applied adhesive or primer, and (3) a visual indication that the adhesive is wet and sufficiently sticky to function at the time of contacting the wallpaper to the wall.